How is mail.ru manifesting in Firefox? As a home page, a page for a new tab or an extension?
How does the Yandex malware show?
Comodo has sponsor deals with Yahoo and Yandex for different parts of the world. The online help
gives the example for Yahoo:
Set my homepage, search engine and browser's new tab to Yahoo (all supported browsers).
I don't know if for parts of the world that get Yandex as sponsor also get mail.ru (both are from Russia) set in their browsers. I'm from West Europe and there we get the Yahoo sponsor when installing CIS when we don't untick it.